Planet Venus Returns to the Evening Sky This Week

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After an absence of just over a year, the "evening star" is about
to reappear.

Venus passed behind the sun, as seen from Earth, back on August
18 in what's known as superior conjunction. Since then, it has
been invisible, mired deep in the brilliant glare of the
sun.

Nonetheless, with each passing day, it has been moving on a slow
course toward the east and pulling slowly away from the sun's
general vicinity. Finally, during this week, the
planet Venus should emerge as an evening "star" very low in
the western twilight.

On Monday evening (Oct. 24), it sets about 23 degrees south of
due west (10 degrees is roughly equal to the width of your fist
held at arm's length) about 50 minutes after sunset. The
sky map of Venus available here shows the planet low in the
southwestern sky.

Only ambitious, skilled observers may
spot the planet then, but by Oct. 30 this will have improved
slightly to 55 minutes, giving less experienced skywatchers a
fighting chance to get their first glimpse.

Here is a challenge to all skywatchers: On Thursday evening (Oct.
27) scan
with binoculars for the planet Mercury a couple of degrees
below Venus, with the two planets hanging a few degrees above the
west-southwestern horizon about 30 minutes after sunset.

Of magnitude -0.3,
Mercury should be visible as a naked-eye object for the
southernmost United States, where it will set nearly an hour
after the sun. For observers at the equator, Mercury will set as
twilight ends, while for Southern Hemisphere observers — in
contrast with those who are north of the equator — Mercury puts
on an excellent evening showing.

Continuing to swing east of the sun during November, Venus will
soon become plainly visible in the west-southwest evening sky,
even to the most casual of observers.

Appearing as a brilliant white starlike object of magnitude –3.9,
our sister planet will set at least an hour after the sun by Nov.
3. It slowly rises higher each evening to adorn the western
evening sky all during the upcoming winter and early spring. By
New Year's Day, it will set as late as 2 1/2 hours after the sun.

Venus reaches its greatest elongation — its greatest angular
distance — 46 degrees to the east of the sun on March 26. From
then, on into mid-April, it will be setting more than four hours
after the sun. It is brightest in mid spring as it heads back
down toward the sun, reaching its greatest brilliancy for this
apparition on April 30 at magnitude –4.5.

Venus, in fact, will be so bright at this stage of the game that
it can be easily perceived with the naked eye in a deep blue,
haze-free afternoon sky. After twilight ends, from a really dark
site, it will be capable of casting faint yet distinct
shadows.

Between now and next May, repeated
observation of Venus with a small telescope will show the
complete range of its phases and disk sizes.

The planet currently appears almost full (95-percent sunlit on
Monday evening), and thus appears as a tiny, dazzling gibbous
disk. It will become noticeably less gibbous by midwinter.

By the last week of March, Venus reaches dichotomy (displaying a
"half moon" shape). Then, for the rest of the spring it displays
a large crescent as it swings near the Earth.

Indeed, those using telescopes will note that while the
Earth-Venus distance is lessening, the apparent size of Venus'
disk will grow, doubling from its present size by March 15. When
it has doubled again in size on May 7, its large crescent shape
should be easily discernable even in steadily held 7-power
binoculars.

As May progresses, our bright sister planet will get rapidly
lower in the twilight, soon to disappear. Venus will actually
start the month almost 40 degrees high in the west at sunset, but
will plummet to a sunset altitude of only around 7 degrees by
month's end (for midnorthern latitudes).

Venus then quickly fades, vanishing from completely from view
during the opening days of June. The stage will then be set for
the exceedingly rare spectacle of Venus appearing to cross in
front of the sun — called a "transit" — at its June 5 inferior
conjunction.

During the third week of June Venus reemerges as a "morning star"
appearing just above the east-northeast horizon. Climbing
progressively higher each morning, Venus will then shine very
prominently in the morning sky right on through the late fall of
2012.

Joe Rao serves as an instructor and guest lecturer at New
York's Hayden Planetarium. He writes about astronomy for The New
York Times and other publications, and he is also an on-camera
meteorologist for News 12 Westchester, New York.